1. Field of the Invention
This invention relates to the cooling of aircraft gas turbine engine exhaust nozzles and more particularly to means for transferring cooling air to cooling air passages of pivotable flaps and seals in a variable throat area exhaust nozzle.
2. Description of Related Art
Aircraft gas turbine engines, particularly of the turbo-jet and turbo-fan types, employ exhaust nozzles having containment members, namely flaps and seals, that are used to contain the hot exhaust flow and produce thrust to propel the aircraft. Cooling of the nozzle is often required in order to provide thermal protection for the nozzle and the rest of the engine. Cooling also helps reduce the infrared signature of the engine and aircraft which is particularly important for military aircraft.
Military aircraft gas turbine engines often employ variable exhaust nozzles having pivotable flaps and seals incorporating liners that are cooled by film or convective cooling or a combination of both. An example of such a nozzle cooling scheme is shown in Warburton U.S. Pat. No. 4,544,098 entitled "Cooled Exhaust Nozzle Flaps" and Sutton et al. U.S. Pat. No. 4,081,137 entitled "Finned Surface Cooled Nozzle". Sutton discloses a convergent/divergent exhaust nozzle having double wall hollow flaps wherein cooling air is supplied to a passage between the double walls and flowed therethrough thereby convectively cooling the hot wall. Sutton further provides outlets for introducing cooling air into the boundary layer to provide film cooling of the hot wall.
Warburton discloses convectively cooled convergent flaps that supply cooling air to respective divergent flaps of an axisymmetric exhaust nozzle. The divergent flaps are film cooled by the cooling air used to convectively cool the convergent flaps, wherein the cooling air is exhausted onto the hot surface of the divergent flap.
As can be seen from these examples of prior art nozzles, containment members are generally hollow having liners that employ, either alone or in combination, means for convective or film cooling. Film cooling means for these liners typically employ slots to introduce film cooling air over what is often a rather extensive axially extending portion of nozzle liner.
One problem associated with the prior art nozzle liner cooling concepts described in the aforementioned patents is that neither the convective cooling nor the slot means for film cooling is a very efficient method of cooling the hot liner surfaces. More efficient methods of cooling would allow the engine to use less cooling air thereby providing savings of weight, cost, and fuel and would also permit the engine to be operated at a higher level of thrust.
Besides requiring greater amounts of cooling air to thermally protect the liners and respective nozzle parts, the prior art liner cooling means cause uneven cooling in the axial direction, subjecting the liners to larger temperature gradients from upstream to downstream ends, particularly during afterburning, creating stresses which can reduce life of the nozzle.
Engine designers are constantly seeking means to reduce the use of expensive, in terms of thrust and fuel consumption, cooling air and strive to reduce, as much as possible, the amount of cooling air used to cool the liners. Slot type film cooling uses relatively large amounts of cooling air as compared to the present invention.
To that end, a nozzle having hollow convergent and divergent flaps and seals was developed as disclosed in related U.S. patent application Ser. No. 07/787,983 entitled "COOLING APPARATUS FOR AIRCRAFT GAS TURBINE ENGINE EXHAUST NOZZLES", invented by John W. Vdoviak et al., filed Nov. 5, 1991, assigned to the same assignee as the present invention, and incorporated herein by reference.
The present invention provides a means to effectively transfer cooling air between relatively pivotable hollow flow containment members, such as respective hollow convergent and divergent flaps and seals. The present invention also provides a supplemental cooling air ejector means to entrain additional air from the engine nozzle bay for cooling the containment members in order to save costly compressor or fan cooling air.